The MEP said that in 2008, it handled 135 environmental emergencies, of which 46 threatened drinking water.

The ministry urged environmental protection departments to investigate potential pollution sources in and around water sources and reserves. It also ordered tighter control of industries that illegally discharge sewage into reserves, including pharmaceuticals, paper-making, smelting and chemicals.

In the latest prominent incident, at least 200,000 people in Yancheng, Jiangsu Province, lost tap water supply for three days last month after a chemical factory illegally dumped the disinfectant phenol into a river.

The mayor promised earlier this month to shut 33 of the city's 317 chemical plants to check contamination.

According to the circular, facilities that aren't related to drinking water supply and protection should be barred from reserve areas.

The MEP also urged water departments to conduct more frequent tests and asked traffic departments to supervise the road transport of hazardous chemicals to prevent leaks into drinking water reserves.